The mechanisms involved in the storage and periodic elimination of urine exhibit marked changes during prenatal and postnatal development. In the young fetus, prior to maturation of the nervous system, urine is presumably eliminated from the urinary bladder by non-neural mechanisms. At later stages of development, micturition is regulated by spinal reflex pathways. As the central nervous system continues to mature during the postnatal period, reflex voiding is brought under voluntary control involving higher brain centers. In adults, injuries or diseases of the nervous system can lead to the reemergence of primitive functions that were prominent early in development but then were suppressed during neural maturation. Therefore, developmental studies of micturition reflex pathways are likely to provide key insights into the mechanisms underlying neurogenic disorders of urinary bladder function in adults. This research proposal will focus on alterations in spinal reflex voiding mechanisms that underlie the maturation of voiding function during the early postnatal period. Aim I). To determine the organization of urinary bladder interneurons and parasympathetic preganglionic neurons in the lumbosacral spinal cord. A combination of transneuronal tracing with pseudorabies virus (Bartha strain) and conventional retrograde dye mapping techniques (Fluorogold) will be utilized. Changes in connectivity between the various spinal elements will be assessed in postnatal rats prior to (P1, P7, P14) and following (P21, P28, P36) the emergence of the spinobulbospinal micturition reflex using design-based stereological techniques. Aim 2). To examine changes in central processing of afferent (A-s and/or C-fiber) information from the lower urinary tract of postnatal rats prior to and following the emergence of the spinobulbospinal micturition reflex. A combination of axonal tracing techniques and Fos protein expression will be utilized. These experiments will determine if A- and/or C-fiber bladder afferents are active during early postnatal development and how afferent information is processed by different neurons in different regions of the spinal cord. Aim 3). To examine the termination pattern, area occupied and morphology of perineal afferent nerve fibers and bulbospinal projections in close apposition to interneurons and/or preganglionic neurons in the lumbosacral spinal cord in postnatal rats prior to and following the emergence of the spinobulbosninal micturition reflex. These studies will determine if perineal afferent projections (Dil or WGA-HRP-labeled) and/or bulbospinal (CRF-IR) projections and varicosities are prominent in the lumbosacral spinal cord and which neuronal populations are in close apposition to afferent or bulbospinal efferent projections. Anatomical studies will be combined with immunoassay for CRF in the lumbosacral spinal cord.